Originally published as Genetics Published Articles Ahead of Print on August 10, 2009.

Genetics, Vol. 183, 619-627, October 2009, Copyright © 2009
doi:10.1534/genetics.109.102848

Homology of Dipteran Bristles and Lepidopteran Scales: Requirement for the Bombyx mori achaete-scute Homologue ASH2

Qingxiang Zhou^*,, Linlin Yu^*, Xingjia Shen, Yinü Li^*, Weihua Xu, Yongzhu Yi and Zhifang Zhang^*,1

^* The Biotechnology Research Institute, National Engineering of Crop Germplasm and Genetic Improvement, Chinese Academy of Agricultural Sciences, Beijing 100081, China, The Sericultural Research Institute, Chinese Academy of Agricultural Sciences, Zhenjiang City, Jiangsu Province 212018, China and State Key Laboratory for Biocontrol and Institute of Entomology, School of Life Sciences, Sun Yat-Sen University, Guangzhou 510275, China

¹ Corresponding author: Biotechnology Research Institute, Chinese Academy of Agricultural Sciences, 12 Zhongguancun South St., Beijing 100081, China.
E-mail: zhifangzhang{at}yahoo.com

Lepidopteran wing scales and Drosophila bristles are considered homologous structures on the basis of the similarities in their cell lineages. However, the molecular mechanisms underlying scale development are essentially unknown as analysis of gene function in Lepidoptera is sorely limited. In this study, we used the Bombyx mori mutant scaleless (sl), which displays a nearly complete loss of wing scales, to explore the mechanism of lepidopteran wing-scale formation. We found that Bm-ASH2, one of four Bombyx achaete-scute homologs, is highly expressed in early pupal wings of wild-type silkworms, but its expression is severely reduced in sl pupal wings. Through molecular characterization of the mutant locus using luciferase and gel shift assays, genetic analysis of recombining populations, and in vivo rescue experiments, we provide evidence that a 26-bp deletion within the Bm-ASH2 promoter is closely linked to the sl locus and leads to loss of Bm-ASH2 expression and the scaleless-wings phenotype. Thus, the Bm-ASH2 appears to play a critical role in scale formation in B. mori. This finding supports the proposed homology of lepidopteran scales and dipteran bristles and provides evidence for conservation of the genetic pathway in scale/bristle development at the level of gene function.

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